1. Field of the Invention
The present invention relates to an illumination device which uses, as light sources, a plurality of semiconductor light-emitting elements such as light-emitting diode chips.
2. Description of the Related Art
Jpn. Pat. Appln. KOKAI Publication No. 2002-94122 discloses an illumination device in which a plurality of light-emitting diode chips are arranged on a base board. In this illumination device, in order to achieve enhancement of light emission efficiency, an increase in light output and elongation in lifetime, heat that is produced by the light-emitting diode chips is made to quickly escape to the base board, thereby enhancing heat radiation properties.
To be more specific, the base board is formed of a metallic material with excellent heat conductivity, such as aluminum. The base board has a flat mounting surface and a plurality of columnar projection portions which project from the mounting surface. An insulation member is stacked on the mounting surface of the base board. The insulation member has recesses at positions corresponding to the projection portions. Through holes, which penetrate the insulation member, are formed at bottoms of the recesses. The projection portions of the base board are put in the through holes. A distal end face of each projection portion is located at the bottom of the recess. A light-emitting diode chip is bonded to the distal end face of each projection portion. Thereby, the light-emitting diode chip is thermally connected to the distal end face of each projection portion.
A wiring pattern is formed on the insulation member. The wiring pattern has a plurality of terminal portions which are located at the bottoms of the recesses. The terminal portions of the wiring pattern and a pair of electrodes of the light-emitting diode chip are electrically connected via bonding wires.
Further, a sealing member is filled in the recesses of the insulation member. The sealing member is formed of a light-transmissive resin. A phosphor is mixed in the sealing member. The sealing member covers the light-emitting diode chips, wiring pattern and boding wires, and protects connection parts between the bonding wires and the electrodes.
In the conventional illumination device disclosed in the above-described Japanese KOKAI Publication, the light-emitting diode chips which produce heat are thermally connected to the projection portions of the metallic base board. Thus, the heat produced by the light-emitting diode chips can directly be conducted to the base board, and the heat can be radiated from the base board to the outside of the illumination device.
However, in the conventional illumination device, although the temperature rise of the light-emitting diode chip can be suppressed, the extraction of light emitted from the light-emitting diode chips is not adequate. Specifically, part of the light emitted from the light-emitting diode chips is absorbed by the phosphor in the sealing member, and is converted to light of some other color and radiated. At this time, part of the light, which is emitted toward the projection portions of the base board, is reflected by the projection portions and is extracted to the outside of the illumination device.
In the conventional illumination device, when the light is extracted, each projection portion is located inside the through hole of the insulation member, and thus the entire periphery of the projection portion is surrounded by the insulation member. As a result, the light that is radiated from the phosphor can be reflected only by a limited part of the distal end face of the projection portion, which is exposed to the periphery of the light-emitting diode chip. Hence, the use of the light from the light-emitting diode chips is not sufficient, and the brightness may become deficient, for example, when purposes of use for general illumination are assumed.